Decision Tree Based Power System
Dynamic Security Assessment
Group 5
Shirley (Xuemeng), Michael (Yu)
3.1.2016
Constraints from previous groups
Group
Base Case
Constraints
1
40GW
PG4<501.46
PG65_2>994.13
2
42.5GW
PG6>753.61
3
45GW
PG6<764.39
47.5GW
PG4<418.49
PG9<1743.54
4
5-2
Our Cases
Case
Load (GW)
Load Percentage
Change (%)
Generation (GW)
Gen. Percentage
Change (%)
1
48
-4.00
48.79
-4.03
2
49
-2.00
49.81
-2.03
3 (Base)
50
0
50.84
0
4
51
2.00
51.86
2.01
Generator output adjustments
Group 4 base
case
- 48GW (PG6=756MW)
50GW case
Scale
(PG4=350MW,
PG6=760MW)
Scale
- 49GW (PG6=758MW)
- 51GW (PG6=762MW)
3
Bus over voltage issue
• Although the power flow of each case successfully
converged…
• 69 over voltage buses in the base case.
• Cause: FIXED shunts. (Shunt
capacitors/inductors.)
Load scaled
while keeping
power factor
constant
Fixed shunts
contribute ~
the same
amount of
reactive
power
Excessive VAR
compensation
Over voltage
problems
(Original case
probably has
higher load
levels)
5-4
TSAT Security Assessment
Case
No. of secure
contingencies
No. of insecure
contingencies
1
340
16
2
335
21
3
335
21
4
332
24
5-5
Decision tree – unpruned vs pruned
Test option – Cross-validation with 10 folds.
Unpruned
Pruned
5-6
Decision tree – unpruned
PG4<=336
5-7
Decision tree –pruned
PG4<=336
5-8
Constraints Summary
Group
Base Case
Constraints
1
40GW
PG4<501.46
PG65_2>994.13
2
42.5GW
PG6>753.61
3
45GW
PG6<764.39
4
47.5GW
PG4<418.49
PG9<1743.54
5
50GW
PG4<336
5-9
Something doesn’t feel right.
OH WAIT…
5-10
Our hypothesis
• In our study, the four cases are basically scaled from the
same case (aside from some minor generation
adjustments).
• As load grows, the system tends to become more
insecure.
• For the same contingency, the four cases will have 5 sets
of potential security assessment results.
5-11
Our hypothesis
Potential
outcome
48GW
49GW
50GW
51GW
1
Secure
Secure
Secure
Secure
2
Secure
Secure
Secure
Insecure
3
Secure
Secure
Insecure
Insecure
4
Secure
Insecure
Insecure
Insecure
5
Insecure
Insecure
Insecure
Insecure
5-12
Our hypothesis
• All attributes, except FB and OB, are equal in a specific case.
• Decision tree first utilizes FB and OB to classify the instances.
• For contingencies that have DIFFERENT security
assessments in the four cases, the decision tree will attempt
to find another attribute to help classify the instances.
• Similar trends are seen in the generator output attributes
(since they are uniformly scaled), the first attribute (PG4) is
selected! Proof: if we switch columns between PG4 and PG6,
the decision tree will use PG6!
5-13
Potential issues
• This will result in the continuing decreasing limit on
Generator 4!
• Assume a contingency with the following outcome:
Case 1:
PG4=336
Case 2:
PG4=343
Case 3:
PG4=350
Case 4:
PG4=357
Secure
Insecure
Insecure
Insecure
The decision tree will tend to choose the constraint
PG4<=336. This will affect the next group.
5-14
A new set of cases…
• In real life system operations, the operating conditions will
change in a much more complicated fashion, instead of
pure scaling of load and generation.
• Based on the previous cases, we altered the output of
generator 11.
Case
1
2
3
4
PG11 (MW)
2000
1699.64
1734.33
1200
5-15
Decision tree – unpruned vs pruned
Test option – Cross-validation with 10 folds.
Unpruned
Pruned
5-16
Decision tree – unpruned
PG4<=336
Limitations?
We cannot use the
information on generator 4
P5-160>113.71
PG4>350
PG4>336
5-17
SPECIAL THANKS TO:
Yongli
Thank you for listening.
18